This application relates to composite compacts of diamond, cubic boron nitride (CBN) or wurtzite boron nitride (WBN) or mixtures thereof for use as a shaping, extruding, cutting, abrading or abrasion resistant material and particularly as a cutting element for rock drilling.
A cluster compact is defined as a cluster of abrasive particles bonded together either (1) in a self-bonded relationship, (2) by means of a bonding medium disposed between the crystals, or (3) by means of some combination of (1) and (2). Reference can be made to U.S. Pat. Nos. 3,136,615; 3,233,988 and 3,609,818 for a detailed disclosure of certain types of compacts and methods for making same. (The disclosures of these patents are hereby incorporated by reference herein.)
A composite compact is defined as a cluster compact bonded to a substrate material such as cemented tungsten carbide. A bond to the substrate can be formed either during or subsequent to the formation of the cluster compact. It is, however, highly preferable to form the bond at high temperatures and high pressures in the stable region of P, T phase diagram of the abrasive particle and comparable to those at which the cluster compact is formed. Reference can be made to U.S. Pat. Nos. 3,743,489; 3,745,623 and 3,767,371 for a detailed disclosure of certain types of composite compacts and methods for making same. (The disclosures of these patents are hereby incorporated by reference herein.)
It has been recently proposed to use synthetic diamond compacts (both cluster and composite) as the cutting elements in rotary drill bits. Such compacts are preferably made in accordance with U.S. Pat. No. 3,745,623. The typical tool design has the abrasive table layer exposed.
One of the problems encountered in the use of the inventions disclosed and claimed in the two patents cross referenced above is that, while the bits provide aggressive cutting action and have abundant room for swarf removal between compact cutting elements, the stresses on each cutting element are severe and cause failures to occur. For example, the carbide pin on which a compact is fixed in certain embodiments may be broken. Also the compact itself is often fractured or cracked. The stresses are due to the fact that the structure of rocks encountered in rock drilling is heterogeneous and thus has layers of varying hardness. These layers cause large variation in the impact loads which are applied to the compact cutting elements during drilling.
Accordingly, it is a feature of this invention to provide an improved composite compact which has improved resistance to fracture for use as drill bits, mining tools, cutting tools and wear pads and improved methods for the manufacture of such compacts.
Another feature of the invention is to provide a composite compact for rock drilling applications which can be operated at faster penetration rates.
Another feature of the invention is to provide a composite compact with enhanced resistance to crack propagation.
Another feature of the invention is to provide an improved method for making a composite compact which has reduced diffusion distances for the transmission of a metallic phase from a cemented carbide mass into the particle mass. Further, this invention overcomes the problems encountered in the manufacture of composite compacts with multiple layers or encapsulation of the lack of adequate accommodation of various components during the HP/HT cycle, which resulted in poorly bonded compacts. This invention produces properly bonded compacts.